Method of shaping a glass article



Sept. 28, y1.965` M. E. NORDBERG y METHOD OF SKHAPING A GLASS ARTICLEFiled Feb. 27.A v1961 United States Patent O York Filed Feb. 27, 1961,Ser. No. 91,705 Claims. (Cl. 65-24) This invention relates toimprovements in the art of reshaping the surface of a glass body toconform with the contour of a surface of a mold or of a second glassbody by contacting said surfaces while heated without the application ofexternal pressure.

In the past it has been found advantageous to conform the surfaces oftwo glass bodies at a relatively low temperature, that is, a temperaturewithin the annealing range of the softer glass, thereby obtainingprecisely matched surface contours without laborious grinding andpolishing operations. By thus conforming such surfaces, accuratelyfitted composite units such as anoptical element, a laminated sheet, orthe like can be produced.

One prior art technique has involved bringing together two glasssurfaces, one of which it was desired to lit or cause to conform to theother, and then applying pressure to urge the surfaces into agreement inthe presence of suliicient heat to release the stress set up by thepressure but without softening the surfaces. When this treatment iscontinued for a predetermined length of time, the surfaces will be foundto be in essential contact and will remain so if the pressure isremoved. By such a procedure it is possible to reduce the number ofinterference fringes between two glass surfaces from an initial value of100 or more to less than 5.

In the conventional bending of sheet glass, one or more sheets areplaced on a refractory base or mold having a desired contour and thebase and the sheet or sheets are heated until the glass, withoutsubstantial change of thickness or other distortion, has conformed tothe contour of the base.

Under the conditions of such methods there is an 0bjectionable tendencyfor the contacting surfaces to adhere and become welded together,particularly if the temperature is in the highest part of the annealingrange and more particularly also if the annealing ranges of the glassesare similar and/or the pressure is unduly long maintained.

Another prior arttechnique, such as described in J. T. Littleton PatentNo. 2,795,084, has involved conformation of a surface of a glass bodywith the contour of a ksurface of another body, such as a metal orrefractory mold or another glass body, by forming on the contactingglass surface or Surfaces a parting film, specifically an vadherentiridized metal oxide film, placingl the bodies together and shaping theglass surface or surfaces, with or without the application of externalpressure while the bodies are heated sufficiently to permit plastic owand conformation of the glass.

While this method permits the utilization of higher temperatures, suchas vtemperatures just below the softening point of the softer glass,thereby permitting conformation of the glass surface or surfaces at anincreased speed, there is an objectionable tendency for the iridizedmetal oxide film to crack due to its brittle nature and its inherentcharacteristic to resist bending, the pattern of which cracks isimparted to and remains on the surface or surfaces of the conformingglass body. While the adhesion of the contacting surfaces may beprevented by this method, laborious grinding and polishing operationsare required to remove the pattern of the cracks of the iridized metaloxide film. l

Still another technique, described in the copending application ofWillard L. Porter, Serial No. 91,704, tiled 7concurrently herewith andassigned to a common assignee,

3,208,839 Patented Sept. 28, 1965 ICC v involves conformation of asurface of a glass body with the contour of another body, such as ametal or refractory mold or another glass body, by applying to thecon'-v tacting glass surface or surfaces an adherent laminar inorganicmineral film, placing the bodies together and shaping the glass surfaceor surfaces, without the application of external pressure, while thebodies are heated sufficiently to permit plastic flow Vand conformationof the glass.

This method also permits utilization of higher temperatures, such astemperatures just below the softening pointv of the softer glass andwhile the film is not brittle and does not impart crack patterns to theconforming glass surface, the method is limited to those compositions ofglass which have a softening point lower than the melting temperature ofthe laminar inorganic mineral film. Conformation of glass having asoftening point higher than the melting temperature of the laminarinorganic mineral results .in the bonding of the mineral film to theglass surface thereby requiring butiing and polishing to remove it.4

It is an object of the present invention to provide an improved methodof conforming glass surfaces, whereby the contacting surfaces can beaccurately matched without adhesion even at temperatures. practically ashigh as the softening point of the softer glass. (Softcning point is thetemperature at which the viscosity of the glass is 10"-6 poises.)

Another object is to conform glass surfaces at an increased speed,particularly if the required amount of conformation be relativelyslight.

Still another object is to attain an increase in the desirable opticalqualities of conformed glass surfaces.

A further object is to conform glass surfaces without impartingirregularities to the surfaces from cracks in the parting film.

A still further object is to conform surfaces of glass bodies havingcompositions whose softening point is above the melting point of laminarinorganic minerals.

In accordance with the invention the method in its broader aspectcomprises conforming the surface of a glass body or bodieswith thecontour of a surface of a glass-adherent body'such as a metal moldand/or another glass body or bodies, by applying to the contacting glasssurface or surfaces a uniform continuous film of colloidal refractorymetallic oxide, which refractory metallic oxide has a meltingtemperature higher than the softening point of glass; placing the bodiestogether and shaping the glass surface lor surfaces while the bodies areheated to a tem- 4 perature above the strain point and below thesofteningpoint of the glass, for a time sufficient to permitsagging orplastic flow and conformation of the glass. (Strain point is thetemperature at which the viscosity of the glass is 10145 poises.)

Ordinarily a porous type refractory mold, which does not adhere toglass, would be used. It is obvious, therefore, that the method of thisinvention would not apply with contoured glass bodies or the surfaces ofthe glass body or bodies, to be conformed, are protected with glasscover plates which are simultaneously conformed. It is also obvious thatthe method of this invention is required in all situations Where theglass body to be conformed is in contact with glass-adherent means ofconformation.

Therefore, when such refractory molds are used, the mold contours arecovered When a metal mold is used in place ofa refractory rnold,consideration must be given in addition to the glass adhesionnotedabove, to compensation of' the mold contour dimensions for thermalexpansion ofthe metal unlessthe application is such" as to permit avariancexin the glass body contour dimensions due to the thermalvexpan'sionoffthe metal. Furthermore, when high temperaturesiarevrequired for the conforming process, the metal moldshould' be heated inan inert atmosphere to yprevent oxidationofits surfaces.

For conformingavplurality of glass bodies the method comprises'applying,` to the'contacting surfaces of the Iglass -b'odies auniformcontinuous film of colloidal refractory metallicoxide,uplacingthe said bodies together and conforming'the'glass surfaces to each otheras wellv as the contourof the refractory or metalmold or anthat shownlin FIG. -l containing three fiat glass bodies with'acollodial'refractorymetallic oxide film applied, all of which-bodiesl arevtoibe conformed tothe shape of the mold andfto' each other? inaccordance with my invention, and

FIG. 3'isanfoblique view of a-mold'similar to those A"shown" in FIGS. '1and 2,.wiih. threefraat glass bndies in' place, illustratingv indexingY-marks by meansof which ma'rks the mold parts and glass bodiesxto` bevconformed maybe aligned-'priorftohe'ating. i v

-In FIG. y1 Va glass-body 1'0,provided with a'colloidal refractorymetallic oxidev `filmVv 152, shown in exaggerated thickness, visdisposedfin va` refractorymold comprising a mold Ybottom l1-'4,yanda'mold top 16, said glass body 10, having` a desired surface contourthe same as mold bottom 14, -beingsupported' on refractory spacers l18,

vwithin heatingchamber .20. A'second glass body 22,-

liavingvpla'nef surfaces is disposedV in said-mold above v the-glassfbody- 10. A-third: glass-body 24, also provided with a colloidalrefractory'metallic oxide film 12,' shown tory metallic oxide in fibril'form, after'which the excess fibrils are removed and the'film is dried.`v

Such? colloidal refractory metallicoxide films `are gen,-

erally'transparent and their thickness is controlled by theeoncentrationof the colloidal'solution as well as the removal of theexcessffibrils.` While a thickness of one continuous layer of fibrils issufficient to prevent adhesion of thev Aglass'surfaces, according to theinvention, greater thicknesses: maybe usedwithoutany difficulties ordisadvantages. Since the fibrils of refractory metallic oxides aregenerally long and thin in shape, some overlapping will occur to obtaina continuous filmI upon the glass surface. It should be noted, however,that such fibrils are usually less than one micron in length and are,therefore, substantially less than one micron-in thickness. l

Some examples of refractory metallic oxidesare: alumina, zirconia,rstannic oxide, titania, as .well as others. Colloidal alumina isparticularly suitablefsince it is readily and economically avalableandthe resulting film is transparent. l v

To Aproduce such colloidal refractory metallicloxide films, thecolloidal metallic oxide should be in powder' form, said -powderconsisting of clusters of minute fibrils desirably having a length ofapproximately .onemicron or less, although larger fibrils will also besuitable.. This powder is then dispersed in water to yield sols ofultimate positively charged fibrils which are strongly attracted to thenegative gla'ss surface.' In accordance with this invention, a colloidalsolution of metallic ,oxide ranging from 0.1% to 2% .by weight isprepared.` The clean glass body is Athen immersed insaid solution'and afilm o f fibrils is depositedv on its surface. The excess fibrils arerinsed off in'distilled l.water leaving a thin uniform layer of fibrilson the glass surface. After.

air drying, such a layer or lfilm will rangeinthickness in exaggeratedthickness and` lhaving `a ldesired. surface v.

contour the same as the mold top 16, -is disposed inthe said mold abovethe glass bodyr22',belo w the mold top 16. f

The three glass bodies together withthe mold and support spacers .are:contained 'within a heating chamber,

vco'rnprisir'iga core 2'6, surrounded by an electrical heating element28, and walls 30,. vcomposed of insulating refractory material. l l

In' FIG'. '2 arnold similar to that shown in FIG. l contains threeglassbodies 132, v34', and 36, having substantially pla'ne -contacting.,surfa'ces, whichglass contacting surfaces o'fglassbodiesiSZ-"a'nd 36,are provided with av uniform eo'ntinuouscolloidal refractory metallicoxide fil-m 38,'shown inexaggeratedthickness.

In FIG V3 amold, ysimilar to those shown in FIGS. 1

y and 2"containsthree glass-bodies with plane contacting surfacesprovide'dwith auniformcontinuous colloidal refractory metallic oxidefilm as -shown inFIG. 2, is

shown withf indexing marks-40, 'on all four sides of mold bottom`I'4,.a'n`d indexing rrrarksfdz,` on all four sides of mold Itop '16. By4'proper' alignment of the indexing marksthemold'parts and glass bodieswill be in position to per-initI conformation'to the desired contour.

A thin colloidal refractory metallic oxide filmsuitable thel glassinaniaqueous colloidal solution of a refracfor'the present-purpose maybeapplied to the-glass by mechanical `means. Such aprocess comprisesimmersing from approximately 50 Angstroms to 0.1 microndepending on theconcentration of the colloidal solution. It should be noted that thefibrils lie fiat ,on the glass surface due to the said attractionbetween thefglass andthe fibrils. v

A film applied in this manner, cannot be. rinsed off lwith water,however, itis not strongly attached' and may be easily rubbed off. Inorder' to harden said film and thereby facilitatepractical handling andto obtain superior adhesion between the film and the glass surface, theglass body with film thereon isv baked at' approximately 450 C. Such abaked film resists mechanical removal even by methods such as scouring.

It has been found thata thin uniform continuous filrnl of colloidalrefractory metallic oxide applied lin accordance -with the methoddescribed above and which. adheres strongly to the :glass surface, whenbaked, will'not permit the glass surface to adhere to vanother glass-surl; `face or to. metal under conditions of heat required to conform'glass surfaces to the' desired shape. Glassfsurfaces, shaped by thenewmethod,therefore, donotad- Y here to each other but can beseparatedafter conformation and are as accurately matched as if the.colloidal refractory metallic oxide film had'been absent andthe-glasssurface does not have any patterns resultin-g from cracks vof the filmor other deformations. v

A` preferred method of carrying out the present invention isillustratedin FIG. lof the drawing. 4The glass bodies 10, 22, and24, arecleaned by any one `of various commercial methods vfor removing dirt,grease, oils and the like, and are subsequently dried. A thin continuousuniform film of colloidal alumina12, is applied to at least one surfaceof each' of the glass bodies .10 and 24, las shown in FIG. l, and it isobvious that such a film may beapplied in the alternative to bothsurfaces Iof glass body 22, with equivalent results. The'glass `body22vis placed'between glass bodies 10vand124, in contact .withthefcolloidalalumina film applied thereto, and all of the'glass bodies'are placed in the refractory mold bottom y means of the' indexing marks40 and 42, shown in FIG.

3, to provide proper alignment among the glass bodies and the moldparts. The assembly is placed in the heating chamber 20, and sufficientelectric current is passed through the heating element 28, to heat themold parts i v14 and 16, and the glass bodies 10, 22, and 24, to justbelow the softening point of the glass, or a temperature at which theviscosity of the glass is slightly above 107'6 poises. This temperatureis then maintained permitting the glass body 22, to sag, through plasticflow into the cavity of mold bottom 14. While the said glass body sagsinto the cavity the glass body' 24, and the mold top 16, lower toproduce the top surface contour of the glass -body 22. When the glassbody has fully conformed to the mold and the contoured glass bodies, theelectric current is interrupted. When the temperature of the glass isbelow the strain point, or the temperature at which the viscosity of theglass is abovek 1014'5 poises, the mold is opened and the glass isremoved.

By a similar procedure two or more pieces of substantially flat glass ofpractically any desired area, such as drawn or rolled sheet glass, maybe shaped at the same time and Atheir contacting surfaces conformed, asshown in FIG. 2.

The example above Aillustrates the use of a porous refractory mold whichwould not require the application of a parting film or colloidalrefractory metallic oxide vfilm between the surfaces of the contouredglass bodies and the contoured surfaces of the mold part-s because thereis no problem with adhesion or welding between glass and porousrefractory materials. If a metal mold is used, where there is anadhesion problem between the metal and glass, the procedure would beidentical with ythe above example except that in addition a colloidalrefractory metallic oxide film would be applied, by the same methodshown in the example, to the upper or mold contacting surface of glassbody 24, and the lower or mold contacting surface of glass body 10.

A typical example of one method of carrying out the present invention isillustrated in FIG. 2 of the drawing and the following description; Twoflat glass sheets 32 and 36, composed of 96% silica glass as describedin United States Patent No. 2,106,744, granted February 1, 1938, to H.P. Hood and M. E. Nordberg. having a softening point of 1500 C. and anannealing point of 910 C., being one foot square in size and I/s" thick,and a third dat glass sheet 34, being o f the same composition and sizeand 1%" thick, were cleansed by washing with lint-free cloths inacetone, alcohol and distilled water baths respectively andsuccessively. The sheets were then air dried. It should be noted thatadditional cleaning by use of an acid bath or by baking at 400 C. to 500C. may be employed if it is desired to remove surface absorbedimpurities. A 0.5% by Weight, colloidal solution of boehmite (AlOOH)alumina consisting of minute fibrils, was prepared by dispersingsaidalumina fibrils in Water and blending same in a commercial blender.Glass sheet 3,2 was then immersed in said colloidal alumina solutionpermittingy said fibrils to be deposited on its surfaces. The excessfibrils were then removed by rinsing the glass sheet in distilled water.The resulting thin uniform continuous film was air dried andsubsequently baked at a temperature of 450 C. After baking, the glasssheet could be easily handled damaging the film. A colloidal aluminafilm was 'then applied, in accordance withl the above procedure, toglass sheet 36. Glass sheets 32, 34 and 36, were arranged one above theother, respectively, upon ka contoured petalite refractory mold bottom14, with all glass contacting surfaces separated by colloidal aluminafilm 38. The mold contour had an approximate chord depth of 2". Apetalite refractory mold top 16, was positioned without rubbing off orotherwise vface imperfections therein, which above the glass sheet 36,and the glass sheets and mold` parts were properly aligned by means of.fthe indexing marks 40 and 42. The entire assembly' was placed upon`v`refractory spacers 18, within heating oven 20, at room temperature andheated at the rate of C. perl hour until the assembly reached atemperature of 970 C. This temperature was then maintained for 3 to 4hours to permit sagging and complete conformation of the glass surfacesto the mold contour. The mold top, by its weight, exerted a force ofapproximately one pound upon each six square inches of glass surface andthis force was found to be suitable. At this timethe assembly was cooledat the rate of 50 C. per hour until the strain point or a temperature ofapproximately 820 C. was reached and thereafter cooled at higher ratesup to 120 C. per hour until room temperature was reached. 'The assemblywas removed from the heating oven and glass sheet 34, was referencedwith the indexing marks for the purpose of trimming the edges whilemaintaining the proper contour. After the glass sheets were removed fromthe mold it was found that despite a slight molecular attraction betweenthe glass surfaces, they sheets readily separated when a razor blade orknife was inserted between them at the edge.

In the instant examp-le, the glass sheets 32 and 36, were used as coverplates for the glass sheet 34, to provide a high optical qualitycontoured sheet, however, if slight mold imperfections can be tolerated,cover plates are not required. The contoured glass sheet dimensions areprimarily controlled by the mold dimensions, therefore the dimensionalaccuracy of the glass contour is limited only by the dimensionalaccuracy of the mold. 1n Apractice a chord depth dimensional toleranceof $0.001" is readily attainable.

The new method may desirably be utilized for the 'production of flat orcurved sheets having accurately matched surface contours, which areadapted to be joined with an interposed sheet of organic plasticmaterial between said surfaces and subsequently sealed to form laminatedsafety glass.

Although the present .invention has been described with respect .tospecific details of certain embodiments thereof, it is not` intendedthat such details be limitations upon the scope of the invention exceptinsofar as set forth in the following claims.

What is claimed is:

1- The method of conforming the surfaces of a glass body to the contoursof the surfaces of other glass-adherent through plastic flow of saidglass body without adhering the glass body surfacesand without producingsurcomprises applying to all contacting glass surfaces a coating of anaqueous solution of colloidal refractory metallic oxide, drying saidcoating to form a thin continuous uniform film of colloidal refractorymetallic oxide, said metallic oxide having a melting temperature higherthan the softening point of the glass of said body, placing said bodiestogether with their surfaces in juxtaposition and shaping said glassbodyto a desired contour while heating it sufficiently to permit plasticflow and conformation of the glass.

2. The method of claim 1 in which the colloidal refractory metallicoxide is colloidal alumina.

3. The method of claim 1 in which the colloidal refractory metallicoxide is colloidal zirconia.

4. The method of simultaneously conforming a plurality of glass bodiesto the contours of the .surfaces of other glass-adherent bodies throughplastic flow of said glass bodies without adhering the surfaces of saidglass bodies and without producing surface imperfections therein, whichcomprises applying to all contacting glass surfaces a coating of anaqueous solution of colloidal refractory metallic oxide, drying saidcoating to form a thin continuous uniform lm of colloidal refractorymetallic oxide, said metallic oxide having a melting temperaturey higherthan the softening point of the glass of said glass bodies,

, 7 y placing s aid plurality of glass bodies Aand said other glass.-adherent bodies together with their surfaces in juxtaposition and"shaping said plurality of glass bodies to a desired contour whileheating them sufficiently to permit plastic adherent thin continuousuniform film ofcolloidal refractory metallic oxide having a meltingtemperature higher than the softening point of the glass of saidbody.

8. The method of conforming the surfaces of glass bodies to thecontoursv of the surfaces of other glass-adherent bodies in contacttherewith; while heated, without adhering them and without producingsurface imperfections, comprising the steps of cleaning said glassbodies,

applying a coating of an aqueous solution of colloidal refractorymetallic oxide to the contacting glass surfaces of said glass bodies,drying said coating to form a thin continuous ,uniform film of colloidalrefractory metallic oxide, baking -said film, said refractory colloidalmetallic oxide having a melting temperature higher than the softenofbaking said film at a temperature-of about 450.C. after said dryingstep.

References Cited-by the Examiner UNITED STATES PATENTS 2,377,849 6/45Binkertet al. V 651-107 XA k2,795,084 6/57 Littleton 65-60 X 2,827,7393/58 Atkeson 65-107 X FOREIGN PATENTS 548,900 12/56 Belgium.v 770,5673,/57 Great Britain.

ing point of said glass bodies, placing the bodiesxtog'ether andshapingthe glass surfaces while the bodiesare heated sufficiently topermit plasticow and conformation` of the glass.

herent bodies in contact therewith, Awhile heated, without adhering themand without producing surface imperfections, comprising Vthe steps ofcleaningv said glassbodies, applying a coating of about 0.1% to 2.0% byWeight aqueous solution of colloidal alumina tothe contacting surfacesof said glass bodies, drying saidco'uting to form a thin continuousuniform film of colloidal alumina, said film having a thickness'rangingfrom about 50 Angstroms lo about 0.1v micron, placing the bodiestogether and shapingy the glass surfaces while the bodies are heatedsufficiently to permit plastic flow` and conformation of the glass.y a 110. The method of claim 9 comprising the further step DoNALL H.sYLvEsTER,y Primary Examiner.

7. IN THE METHOD OF CONFORMING AT LEAST ONE GLASS BODY BY HEATING WHILEIN CONTACT WITH MEANS PRODUCING REQUISITE DEFORMATION THEREIN, THEIMPROVEMENT WHICH COMPRISES THE STEP OF APPLYING TO ALL CONTACTING GLASSSURFACES AN ADHERENT THIN CONTINUOUS UNIFORM FILM OF COLLOIDALREFRACTORY METALLIC OXIDE HAVING A MELTING TEMPERATURE HIGHER THAN THESOFTENING POINT OF THE GLASS OF SAID BODY.